Impedance element for protective relay systems



y 1934- L. N. CRICHTON ET AL 7 1,967,201

IMPEDANCE ELEMENT FOR PROTECTIVE RELAY SYSTEMS Original Filed March 20, 1930 WITNESSES: INYENTORS Leslze N; Crzchlon and $0 4; HerbYeri G. Graves Jr. $2. 6 W

ATTORNEY Patented July 17, 1934 IMPEDANCE ELEMENT FOR PROTECTIVE RELAY SYSTEMS Leslie N. Crichton, Livingston, N. J., and Herbert G. Graves, J12, Upper Darby, Pa, assignors to Westinghouse Electric and Manufacturing Company, a corporation of Pennsylvania Original application March 20, 1930, Serial No. 437,924. Divided and this application October 6, 1933, Serial No. 692,472

7 Claims. (01. 175-4594) This application is a division of our parent-application Serial No. 437,924, filed March 20, 1930 for Protective relay systems, which-parent-application was a substitute for, and a continua- I tion-in-part of, our application Serial No. 393,433,

filed September 18, 1929. v i

Our invention concerns protective systems for electric-distribution circuits and, more particularly, protective systems for electric-railway power 10 circuits. 7

The principal objects of our invention are to effect the prompt'isolation of any trolley feeder of an electric-railway distribution circuit on which a fault occurs and, at the same time, to

cuit.

Another object of our invention is to provide means for obviating the effect of load currents o the operation of the protective relays.

A more specific object of our present invention is to provide an improved impedance element for a protective relay system such as that referred to above.

With the foregoing and other objects in view, our invention consists in the apparatus and combinations hereinafter described and claimed, and illustrated in the accompanying drawing, the single figure of which is a diagrammatic view of circuits and apparatus embodying our invention.

The usual alternating-current electric-distribution system for' railway service comprises a high-voltage transmission line, such as that shown at 10. Energy is supplied to the motive equipment of the railway from trolley conductors or contact lines 12, 13, 14 and 15. The contact lines are adapted to be sectionalized by circuit breakers located at conve'nientstations along the line of the railway, such as 23, 24, 25, 26.

When the circuit breakers 23 to 26 are closed, the conductors 12 to 15 will be connected to the bus 28 which is connected to an energy-supply-' ing electrical translating device, such as one ter-' minal of the secondary winding of a step-down transformer, as shown'at 31, through a circuit breaker which is indicated schematically, together with its relay control equipment, at 33. The other terminal of the secondary winding of the step-down transformer is adapted to be grounded. The primary windings of the transformers are connected to the high-voltage transmission line 10. The circuit breaker42 is adapted to connect the bus 28 to another bus (not shown) at the same substation.

In a system such as that described hereinabove,

maintain service on all other portions of the cirit is requisite that faults occurring on trolleyconductors or, for that matter, on the substation buses, shall be isolated with the utmost possible dispatch. Such operation is necessaryin order to avoid interference with communication circults in the neighborhood of the railway. It is equally important, furthermore, that sound conductors remain connected to their source of energy, even at times of fault on other conductors,

-in order to avoid unnecessary interruptions in service. It is desirable, therefore, that a protective system for a railway distribution circuit be characterized by high speed in operation and the utmost selectivity possible, and, at the same time be dependent upon load conditions and upon the capacity of the connected generators, which are commonly added to the system and disconnected therefrom with the coming and passing of peakload conditions of the railway system, so that the maximum load current of the peak-load coriditions may be more than many fault-currents obtained during off-peak conditions.

It is the general object of our invention to provide a protective system having such characteristics and, addition, to provide protection 30 against the occurrence of a fault of any possible type- The protective apparatus of our invention includes a high-speed or instantaneous impedance-responsive or fault-distance-responsive re- 5 lay 50 and a high-speed'or instantaneous directional relay 51 which have their contacts 52 and 53 connected in series with a circuit including a source of energy, such as the battery 54, and

the trip coil 55 of the circuit breaker 23. The impedance relay 50 is an improvement uponthe impedance relay described in the patent to Crichton, No. 1,292,584 and comprises an actuating winding 54', which is adapted to be energized in accordance with the current traversing the conductor 12 to be isolated, and two restraining windings'55' and 55" adapted to be energized in accordance with the voltage on said conductor. The current and voltage windings 54' and 55, 55" are energized, respectively, from the current and potential transformers 56 and 57 associated with the conductor 12 and bus 28.

The voltage windings 55' and 55" are made in two parts with separate armatures, and with dephasing means such as a choke coil 57' in series with the winding 55 and a resistor 57" in series with the other winding 55", in order to increase the number or frequency of the force-pulsations on the relay 50, and also to reduce the magnitude of each impulse thus reducing the tendency toward. chattering, which is a serious difliculty in rection of energy flow, the relay 51 will tend to the design of impedance relays when they are close its contact 53. This follows from the submade instantaneous, by which we mean that stantially in-phase relation between the fluxes their .averagetime of operation is Within Irom produced by the currentstraversing the bus 28 cycle to cycle, or within 1 cycle on a (SO-cycle '"and thecircuit 12, by which we mean that the system, or even less time, from the instant when. directional winding 61 which is nearer the conthe relay setting is exceeded. 7 tact 53' makes a south pole at substantially the In addition to the current and voltage wind-t same half-cycle that the polarizing winding 60 ings, the impedance relay 50-isa1so provided withc-makes a north pole. Under these conditions, a load-presetting device comprising the windinghowever, the closing of the contact 53 is ineffec- 58 connected in'series with the current winding tive so long as the impedance-relay contact 52 5 1. The armature associated with therwinding remainsopen) When the direction of energy 53 i resiliently cu d tothe Contact 52 'Of'thG-aflOW 1511:0111. the trolley conductors towards the r l y 50 by means p i e 58", for pl "bus 28, the phase relations or the voltage and cur-' so that, when the winding 58 is energized, an rentw'ill be altered, and the fluxes produced by additional restraining force isi applied toxthe'con j the: windings 60 and 61 of the relay 51 will pretact of the relay 50, requiringia strongervenerglzw: ve'nt the closing of its contact 53, or will instantion of the current-responsive actuating winding taneou'sl-y-open-the contact 53 if it was previousor a weaker energization of the voltage-,responlyclosed; that is, the remote directional winding sive restraining winding to cause the closing of the 61" makes a south pole at substantially the same contact 52 of theimped n y: 1A -d y: .h3i1f0yCl8-i hat: the polarizing winding 6O vmakes .mdevice, such as a-dashpot 59, vpreventsithe load nanonth-pOlG;

-presettingdevice .from responding immediately to 1 :While the impedance relay 50 Jand the'direcuflhailges the-"Current vflovil-iilgl ymtional relay 51-areboth:instantaneous, as'disline 12.

-; tinguished 'rrom-priorvdevices in which rthe relay Theinstan aneousdirec i n l-01" r v rs n ey at the end of the line-section nearest itheiEfault ay- Shown at D S an E-shapede had 130151211 13 its associated circuitebreakeribefore ma n c-cir i r-y -5 and p i wthe-:morex:remotez relays could discriminate be- 1 3"p v 9 ing armature 51'. H11W8111 thesound-and faiiltydine sections, itiwill The directional windings 61 and 61' 0f the IBVerS be understood that the directional relay'firyshoulfl -ener y relay 51 are d p on Outer legs operate tobpen its contact '53risubstantially as ;thei yoke=59a and, are energized from; the clll'lentg-rquigkly as, or ferablyiquickerrthamuthe'imbus 28,: and in the reverse direction-is disposed on, fond-his purpose,

transfo 56in h r ll y Windingfii pedance relayoperates to close its: contact 52, nd b tflpp fi y Soihailone or,r;in genera-1, within about "M; cycle oreverrless makesia; north polewhile the .other makesasouth times It .-wi1l be furtheritunderstood'tthatgiany pole :at substantially. the same instant.

polarizingd flpwhichi-iaffords anshifting orgad 'justing' shuntsz'liiimimay be'used in as foricomparisontogvenable the reverse-energy; *connectiomwith -the reversei 'current' relay, 51, if .xrelay to= discriminate betw the e y w in it is notr'convenient tosmakethe-zinertia 01* the the-trolleyline 12 in the direction away from the r'ro'oking switch-arm r armature 51 -suflicient necessary anti-chattering device, such asephasethe inner, leg of the-ryokew59aaandiis connected, As-shown in rthe"dna ing;i'tfie m k e m 51' 0 d t0.- the "embodiment of 01-11 inv nt of the polarized relay 51 may be providedcwith a Sh ine-the-drarwmgs to Ive-energized ifmm weight or'a biasing spring=-61uforthe purpose of current-t 'a sfor er 6 n t wS pp i i making ithe openingraction 0t thecrelaysome; 23eWhiCh fi its-being 'r -whatzmore; rap'id:'than its closingnaction,=in'order giZd from the Potential mer 57-; as we; toeenabl'e the polarizingtzrelay 5'1 to move faster I atfirst connected it. The reason 1 01: thiS'1S that qthanqthejmpedance relay on; pr per :occasion, .a" severe fault will so pullidowncthe voltageethat-e as heretoforg explained.

- the polarizing ondiscr-imator-y effect-oi the voltage C011iofithereverse'enelgykrelayi reverse energyrelay 51, we, also provide a'idiffer- In addition to the impedance relay 50 .and the t nected by, us,would sometimes bet-masked bythe entiw13-currentg're1ay 2:, h1 h is adapted to be e D Strengthflfihe ener ized, bysth'e difierence between the current directional.coilsi61at timesoflfaults, whereas:our p the transformer 31 t t bu 23 epresent bus-supply current-responsive. polarizing landvthesum oflthgcurremsifi n the other 139 Ill .,iquickpositive operation which must bembtainedfifthepolarizedrelay is to bezetlective to'open its line circuit breaker of any: line-section inewhich;

- :the fault-current flows toward the adjacent -bus,

-when-rthe, normalpowen current ds-away-.-f-rom,

:1 :thebus.

ci1 o r Polarizing current -Qe 'ductors connected to the-bus 28. .t The energizatimes n: Such current is needed" giving lthei iiutioh of: the. relay 62 is-effected bysuitablehbridge connections which receive 7 energy Whenever the current flowing in: the bus-supply :current transformer 63 is not-substantially"equal toithe sum of the current in-aplurality of current transformer-s 64 which are connected in the four-trolley-' conductors -12 to 15'and in the bus-tie circuit ofthe bus-tie'circuit breaker HI -Therelay 62 contacts 53 andthus prevent the-tripping of the .vThew:busesupply:=.-.current transtorrner 63 placed in: the groundedneutral secondarvtermi:

V nal circuit ofethetransformer 31 ,.ratheri than on thehigh-pctentialor bus terrninal of-ethe'transformersecondarywinding, so as to. avoid.-the-ne :-.cessityrfor a high-voltage (311111 6111): trarrstormer; F

.-Connections=.-are so made to the i windings Gl and 61! ofvthe"reverseeenergyirrelay 51- that,-

thewtrolley conductor, 12,: whichniswthe normal di-x 'hasrfive contacts 65 which are-adapted'to control the circuits to the respective tripping coils 55 of the four trolley-line circuit breakers 23 to 26, as

well as the tripping coil 66 of ,the transformer circuit-breaker 33 .andthe tripping coil 6'7 of the bus-tiedircuit-breaker 42, so as to completely isolate" the bus '28 in the eventwof a. bus fault.

Having described the apparatus which we utilize for the protection 05a. railway distribution system of the type-described, weshall-now exeplain the method of its operation under different conditions.

The'impedance relay has the well-known characteristic of operating when the impedance ratio of voltage to current falls below a predetermined minimum value; and by impedance we mean to include either the entire impedance of the line-section or any significant component thereof. The impedance relay 50 constitutes a means for estimating, and responding to, the distance of a fault from the sectionalizing sta tion, because, at times of fault, the impedance of the line itself constitutes practically the entire impedance of the circuit, being almost wholl reactive, as is well known.

The addition of the load-presetting coil 58 to the impedance relay does not affect its impedance- V responsive characteristic butchanges the setting of the relay in accordance with the value of the current traversing the circuit immediately preceding the fault, instantaneous operation of the pre-setting coil 58 being prevented by the spring and dashpot connection 58, 59. It is characteristic of load currents that they increase to their maximum value with less rapidity than fault currents. In ordinary practice, too, the load current will be built up by small increments as additional units are connected to the load circuit. As the load current thus builds up, usually accompanied by a corresponding increase in the total generator capacity connected to the line, the load-presetting coil is energized more strongly and exerts a greater restraining force on the movable element of the relay 50, which is thereby prevented from operating. In the case of a rapid increase in the current traversing the circuit, however, as at times of fault, the relay 50 will be operated because of the increased energization of its actuating coil 54, since the restraining effect of the presetting element 58 is not immediately effective but requires that a certain time element, introduced by the dash pot 59, elapse before the presetting element becomes effective. It will be understood, however, that our load-presetting attachment is not always needed, and we do not desire to limit ourselves to its use.

It will be apparent, from the foregoing explanation, that the impedance relay 50, with the load presetting device 58, 59, is responsive only to the fault-current increments and, since the normal load current introduces a restraining effect proportional to its magnitude, the operation of the relay 50 is compensated for changes in the magnitude of the load connected to the circuit. Our system is thus freed from a serious disadvantage of earlier systems, namely, that, at times of heavy load, a high-impedance fault may trip the circuit breakers and, at times of light load, a low-impedance fault may not produce sufficient fault current to trip the circuit breakers.

The directional relay 51 operates, in the manner described heretofore, to prevent the tripping of the circuit breakers at all times when energy flows in the direction towards the adjacent sectionalizing bus at the switching station. When a fault occurs near the end of any trolley-conductor 12, 13, 14 or 15, the direction of energy flows from all of the other conductors into that end of the faulty conductor will be toward the adjacent sectionalizing bus at that end, and, by the use of the directional relay 51, this fact is made use of to prevent the tripping of the circuit breakers in the sound conductors.

The differential relay 62 operates when a fault occurs On the substation bus 28, with the result that the current supplied to the bus from the transformerv 31 differs from the'total current supplied from the bus 28 to the conductors 12 to 15 and to the bus-tie circuit breaker 42; In such circumstances, the relay 62 causes the tripping of Cir . Alclosed condition of both of the relays 50 and 51, of course, indicates a low-impedance fault, and the fact that the fault has occurred on the conductor with which the relays are associated. Under these conditions, the sectionalizing circuit breaker. is immediately opened and the faulty line isolated. The impedance relay 50 measures the apparent impedance of the trol- Icy-conductor circuit, automatically making adjustment, by means of the presetting device, for any load current then being supplied. This relay, then, determines the advisability of tripping the breaker from the standpoint of the current fed to the line. The directional relay 51 determines whether the energy supplied to the conductor is in the direction characteristic of a fault, and prevents the tripping of any circuit breaker in a line in which energy is not flowing away from the bus.

While we have particularly described our protective relay system in an application to rail- Way feeder circuits, it will be understood that the invention is applicable to other electric sys' tems of transmission or distribution of power. Since alterations in the system of our invention, as shown and described herein, will, no doubt, ocour to others, we do not wish to be limited to the specific embodiment disclosed, except as necese sitated by the scope of the claims.

The system of cutting out a line in which a fault occurs, as hereinabove described, constitutes the subject-matter of our parent application Serial No. 437,924, heretofore mentioned, Our directional relay element constitutes the tutes the subject-matter of our parent application Serial No. 692,473, filed simultaneously herewith.

We-claim as our invention:

1. An instantaneous alternating-current impedance relay comprising electro-magnet-and-armature means for developing actuating impulses responsive to current, and electro-magnet-andarmature means for developing restraining im pulses responsive to voltage, characterized by the ture for each, a mechanical connection therebetween whereby the total pull is balanced, and relay-contacts carried by said mechanical connection, characterized by one of said electromagnets being a current winding, others of said electro-magnets being voltage windings, and

meansifor:.shifting.;thez.phase of: the currents L4. In angimpedance relay; the "combination of a plurality om 'electro-magnets; a separate arma-w" ture for: each,';a mechanical connection therebe-1 tween: whereby the total pull is balanced, "and ring voltage-responsive means for providing subrelay-contacts carried by said. mechanical conone of said voltage windings, said means comprisving animpedance connected in series with one o;

I *said voltage windings.

5. Azquick-acting relay-including two electromagnet-"means both responding to the same alternating-current quantity. for developing two 'pulsatory relayoperating-forces pulling together *but out of. phasevvith: each other, said means including phase-shifting means associated therewithzforaccomplishing the stated result, other 'meansxfor developing a: different relay-operating force in opposition to said first two-forces; and

-:contact-carrying means the *position {of which is changed accordingto which of the opposing forces 151111116 greater.

,6. An instantaneous impedance relay comprisdivided dephasedseparate magnetic flux paths, a

dissimilarlyenergized electrcimagnetic means energized dissimilarly from' said voltage-responsive means, and structural means for: opposing the magnetic pulls developed by said first two means.

7: An instantaneous impedance relay comprisfmg voltage-responsive means for producing subdivided dephased separate; magnetic fiux paths,

--a current-coil means, and structural means for p opposing the magnetic pulls developed by said firstvtwo means.

LESLIE NirCRICI-ITON. HERBERT C. GRAVES JR. 

